CORRESPONDENCE
Darwin’s Statements on Reversion or Atavism Xiuju Li,1,2 and Yongsheng Liu1,2* 1
Henan Institute of Science and Technology, Xinxiang, China Faculty of Medicine, Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
2
Manuscript Received: 17 November 2013; Manuscript Accepted: 24 March 2014
TO THE EDITOR: We read with great interest the article “Annals of morphology. Atavisms: Phylogenetic lazarus?” by Zanni and Opitz [2013]. This is a well-written review that considers the concept of atavism from a developmental, evolutionary, and genetic perspective. But it contains no reference to Darwin’s two volumes on “The Variation of Animals and Plants under Domestication” [Darwin, 1868]. It is in this book that Darwin comes nearest to the subject of atavism, and discusses it in one long chapter entitled “reversion or atavism” (Chapter 13). In using the term “reversion,” we believe that Darwin meant the sudden appearance of individuals with characteristics that were present in some progenitor. He appeared to be convinced of the importance of reversion, and regarded it as an essential part of the general law of inheritance. He noted that “the tendency to reversion is often induced by a change of conditions, and in the plainest manner by crossing.” By which we believe he meant, a change of environmental conditions would affect the reproductive system. A crossing of two distinct breeds is also a potent means of inducing reversion. He conducted several of his experiments on reversion in both pigeons and poultry. In crossing two different pigeon varieties, he obtained offspring that did not resemble either parent but demonstrated the slaty color or the double black wing bars of the putative ancestral rock dove. He also crossed a White Silkie hen with a Spanish cock which is perfectly black. “As the cocks grew old one… became a gorgeous bird. When stalking about it closely resembled the wild Gallus bankiva, but with the red feathers rather darker.” It should be noted that Darwin’s experiment in poultry was confirmed by Davenport [1910], who made the same cross with the same result. Darwin’s breeding experiments led him to conclude that reversion did indeed occur. To explain the mechanism of reversion and many other genetic phenomena, Darwin elaborated his Pangenesis hypothesis. He proposed that cells are able to “throw off” numerous, minute molecules he called gemmules, which are capable of self-replication, circulation through the body, and transmission from the parents to the offspring. In addition, gemmules, like seeds in the earth and buds in the bark of a tree, are capable of dormancy. They are often transmitted in a dormant state during many generations and are then developed. According to Pangenesis, reversion was due to the long-dormant ancestral gemmules becoming active after the transmission of many generations [Liu, 2005].
Ó 2014 Wiley Periodicals, Inc.
How to Cite this Article: Li X, Liu Y. 2014. Darwin’s statements on reversion or atavism. Am J Med Genet Part A. 9999:1–2.
It appears to us that Darwin’s Pangenesis contains a great truth. The discovery of circulating DNA, mRNA, and microRNAs provides strong evidence for the chemical existence of Darwin’s hypothetical gemmules [Liu, 2008]. Belyaev et al. [1981] demonstrated a fused gene in the house mouse with about 6% of mutants produced wild-type young, and after several generations, 1% reverting to the mutant type. They suggested that inactive (“dormant”) genes may be activated and reverted toward an inactive state. A similar reliance on gene activation–inactivation had been implied by Zuckerkandl and Pauling [1962], who first formulated the “dormant gene” hypothesis. Obviously, these modern ideas are consistent with Darwin’s Pangenetic explanation. Zanni and Opitz [2013] stated that Darwin briefly cited Lord Morton’s mare as an example of “reversion” in his “The Origin of Species” [Darwin, 1859]. But in his “The Variation of Animals and Plants under Domestication” [Darwin, 1868], he also cited Lord Morton’s mare as an example of “the direct action of the male element on the female form” (later known as “telegony”), a discredited genetic phenomenon that a previous male may influence the characteristics of offspring subsequently borne by the same female to another male. When Darwin discussed telegony he brought up the case of Lord Morton’s mare. He concluded that “there can be no doubt that the quagga affected the character of the offspring subsequently begot by the black Arabian horse.” Recently, a possible molecular mechanism for the phenomenon of telegony has been proposed, based on the discovery of fetal genes in mother’s blood and the penetration of somatic cells by sperm [Liu, 2013].
Correspondence to: Yongsheng Liu, Henan Institute of Science and Technology, Xinxiang 453003, China. E-mail: [email protected] Article first published online in Wiley Online Library (wileyonlinelibrary.com): 00 Month 2014 DOI 10.1002/ajmg.a.36581
1
2
AMERICAN JOURNAL OF MEDICAL GENETICS PART A
REFERENCES
Liu Y-S. 2005. Reversion: Going back to Darwin’s works. Trends Plant Sci 10:459–460.
Belyaev DK, Ruvinsky AO, Borodin PM. 1981. Inheritance of alternative states of the fused gene in mice. J Hered 72:107–112.
Liu Y-S. 2008. A new perspective on Darwin’s Pangenesis. Biol Rev Camb Philos Soc 83:141–149.
Darwin C. 1859. On the origin of species by means of natural selection or the preservation of favoured races in the struggle for life. London: John Murray.
Liu Y-S. 2013. Fetal genes in mother’s blood: A novel mechanism for telegony? Gene 524:414–416.
Darwin C. 1868. The variation of animals and plants under domestication. London: John Murray. Davenport CB. 1910. The new views about reversion. Proc Am Philos Soc 49:291–296.
Zanni G, Opitz JM. 2013. Annals of morphology. Atavisms: Phylogenetic lazarus? Am J Med Genet Part A 161A:2822–2835. Zuckerkandl E, Pauling L. 1962. Molecular disease evolution and genetic heterogeneity. In: Kasha M, Pullman B, editors. Horizons in biochemistry. New York: Academic Press. pp. 148–173.
Darwin’s Statements on Reversion or Atavism Xiuju Li,1,2 and Yongsheng Liu1,2* 1
Henan Institute of Science and Technology, Xinxiang, China Faculty of Medicine, Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
2
Manuscript Received: 17 November 2013; Manuscript Accepted: 24 March 2014
TO THE EDITOR: We read with great interest the article “Annals of morphology. Atavisms: Phylogenetic lazarus?” by Zanni and Opitz [2013]. This is a well-written review that considers the concept of atavism from a developmental, evolutionary, and genetic perspective. But it contains no reference to Darwin’s two volumes on “The Variation of Animals and Plants under Domestication” [Darwin, 1868]. It is in this book that Darwin comes nearest to the subject of atavism, and discusses it in one long chapter entitled “reversion or atavism” (Chapter 13). In using the term “reversion,” we believe that Darwin meant the sudden appearance of individuals with characteristics that were present in some progenitor. He appeared to be convinced of the importance of reversion, and regarded it as an essential part of the general law of inheritance. He noted that “the tendency to reversion is often induced by a change of conditions, and in the plainest manner by crossing.” By which we believe he meant, a change of environmental conditions would affect the reproductive system. A crossing of two distinct breeds is also a potent means of inducing reversion. He conducted several of his experiments on reversion in both pigeons and poultry. In crossing two different pigeon varieties, he obtained offspring that did not resemble either parent but demonstrated the slaty color or the double black wing bars of the putative ancestral rock dove. He also crossed a White Silkie hen with a Spanish cock which is perfectly black. “As the cocks grew old one… became a gorgeous bird. When stalking about it closely resembled the wild Gallus bankiva, but with the red feathers rather darker.” It should be noted that Darwin’s experiment in poultry was confirmed by Davenport [1910], who made the same cross with the same result. Darwin’s breeding experiments led him to conclude that reversion did indeed occur. To explain the mechanism of reversion and many other genetic phenomena, Darwin elaborated his Pangenesis hypothesis. He proposed that cells are able to “throw off” numerous, minute molecules he called gemmules, which are capable of self-replication, circulation through the body, and transmission from the parents to the offspring. In addition, gemmules, like seeds in the earth and buds in the bark of a tree, are capable of dormancy. They are often transmitted in a dormant state during many generations and are then developed. According to Pangenesis, reversion was due to the long-dormant ancestral gemmules becoming active after the transmission of many generations [Liu, 2005].
Ó 2014 Wiley Periodicals, Inc.
How to Cite this Article: Li X, Liu Y. 2014. Darwin’s statements on reversion or atavism. Am J Med Genet Part A. 9999:1–2.
It appears to us that Darwin’s Pangenesis contains a great truth. The discovery of circulating DNA, mRNA, and microRNAs provides strong evidence for the chemical existence of Darwin’s hypothetical gemmules [Liu, 2008]. Belyaev et al. [1981] demonstrated a fused gene in the house mouse with about 6% of mutants produced wild-type young, and after several generations, 1% reverting to the mutant type. They suggested that inactive (“dormant”) genes may be activated and reverted toward an inactive state. A similar reliance on gene activation–inactivation had been implied by Zuckerkandl and Pauling [1962], who first formulated the “dormant gene” hypothesis. Obviously, these modern ideas are consistent with Darwin’s Pangenetic explanation. Zanni and Opitz [2013] stated that Darwin briefly cited Lord Morton’s mare as an example of “reversion” in his “The Origin of Species” [Darwin, 1859]. But in his “The Variation of Animals and Plants under Domestication” [Darwin, 1868], he also cited Lord Morton’s mare as an example of “the direct action of the male element on the female form” (later known as “telegony”), a discredited genetic phenomenon that a previous male may influence the characteristics of offspring subsequently borne by the same female to another male. When Darwin discussed telegony he brought up the case of Lord Morton’s mare. He concluded that “there can be no doubt that the quagga affected the character of the offspring subsequently begot by the black Arabian horse.” Recently, a possible molecular mechanism for the phenomenon of telegony has been proposed, based on the discovery of fetal genes in mother’s blood and the penetration of somatic cells by sperm [Liu, 2013].
Correspondence to: Yongsheng Liu, Henan Institute of Science and Technology, Xinxiang 453003, China. E-mail: [email protected] Article first published online in Wiley Online Library (wileyonlinelibrary.com): 00 Month 2014 DOI 10.1002/ajmg.a.36581
1
2
AMERICAN JOURNAL OF MEDICAL GENETICS PART A
REFERENCES
Liu Y-S. 2005. Reversion: Going back to Darwin’s works. Trends Plant Sci 10:459–460.
Belyaev DK, Ruvinsky AO, Borodin PM. 1981. Inheritance of alternative states of the fused gene in mice. J Hered 72:107–112.
Liu Y-S. 2008. A new perspective on Darwin’s Pangenesis. Biol Rev Camb Philos Soc 83:141–149.
Darwin C. 1859. On the origin of species by means of natural selection or the preservation of favoured races in the struggle for life. London: John Murray.
Liu Y-S. 2013. Fetal genes in mother’s blood: A novel mechanism for telegony? Gene 524:414–416.
Darwin C. 1868. The variation of animals and plants under domestication. London: John Murray. Davenport CB. 1910. The new views about reversion. Proc Am Philos Soc 49:291–296.
Zanni G, Opitz JM. 2013. Annals of morphology. Atavisms: Phylogenetic lazarus? Am J Med Genet Part A 161A:2822–2835. Zuckerkandl E, Pauling L. 1962. Molecular disease evolution and genetic heterogeneity. In: Kasha M, Pullman B, editors. Horizons in biochemistry. New York: Academic Press. pp. 148–173.
